Treatment of residual liquors



Patented Nov. 7, 1933 UNITED STATES.

PATENT GFFECE Mcleefe, Plattsburgh, N.

Corporation,

Bradley-McKeefe lassignors to New York,

N. Y., a corporation of New York Application April 2, 1928. Serial No. 266,863

19 Claims.

This invention relates to improvements in the treatment of residual liquor resulting from the cooking of wood, etc. in a cooking liquor containing sodium sulfite or other sulfur bearing compounds of sodium and to the production ofsultes such as sodium sulte adapted for use in such cooking liquor.

The invention includes an improved process of ltreating solutions containing sodium suld, and

o particularly solutions containing sodium carbonate and sodium sulfd, to effect simultaneous sulting of such solutions and elimination of the sulid sulfur therefrom, thereby producing directly, as a result of the combined sulting and suld removal', a solution containing sodium sulte. This combined suliting and suld removal is accomplished by treating the solution containing sodium suld with a suitable sulte, e. g., ammonium sulte, which Will react With the sodium sulrld to form sodium sulte and a volatile suld (i. e., hydrogen sulid or ammonium suliid) which is driven oi from the solution together with ammonia. Other sultes such as magnesium sulte or calcium sulte can be used under suitable temperature conditions, or mixtures thereof with ammonium sulte.

When a furnace product containing sodium carbonate and sodium suld is dissolved in Water and the cool solution suliited With gaseous SO2 9i a considerable amount of thiosulfate is usually formed, and large amounts of thiosulfate are objectionable in regenerated sulte cooking liquors, and even small amounts of thiosulfate are obiectionable in acid sodium suliite cooking liquors. In order to avoid the formation of such objectionable amounts of thiosulfate by directly sulting such solutions it has been proposed to irst remove the suld sulfur of the solution and then subsequently to sulte the suld free solution.V 43 The present invention enables such solutions containing sodium suliid to be directly sulted and the suld sulfur simultaneously removed Without the formation of objectionable amounts of thiosulfate.

"sa The present invention is based upon the discovery that such a solution (i. e. containing sodium sulfid, e. g. sodium carbonate and a substantial but lesser amount of sodium suld) can r be treated so as to form a volatile suld from sulfur content of the sodium sulijld and so as to remove such volatile suliid from the solutionand so as to convert a portion of the sodium content of the sodium suld'into sodium subite, providing the solution isv maintained substantially nonacid in character While introducing the sulte radicle, .thereby providing a solution which contains more sodium present as a sulte of sodium than as a thiosulfate of sodium. The amount of 60 thiosulfate-sulfur in such .resulting solution in proportion to the amount of sulte-sulfur therein can be thereby suitably regulated.

The volatile suld removed from the solution may be oxidized to form a suliite and such sulte may be regained in any suitable manner and may be employed in forming a sulfite of sodium, or such suld may be otherwise utilized or treated.

According to one embodiment of the invention, we prepare such a solution containing sodium carbonate and sodium suld by treating such a furnace product with a suitable amount of Water so as to produce a relatively concentrated solution. By employing hot Water, or otherwise obtaining a hot solution, the concentrated solution may be obtained at a temperature of between, for eX- ample, 60 to 100 degrees centigrade.

Ammonium suliite in concentrated and cool solution, and with somefree ammonia therein if desired, is added to the hot concentrated solution containing sodium carbonate and sodium suld in small and regulated amounts until at least, or preferably more than, as much has been added as is chemically equivalent to the sodium suld, such as shown by the equation:

and the solution is boiled and agitated, e. g., by introducing steam, during the addition of the ammonium sulte, and such boiling and agitation 1.

is continued until all or nearly all volatile suld thus formed has been removed from the solution. More ammonium sulte than is chemically equivalent to the sodium suliid, for example around 50% more or a larger amount up to an 1 amount which is chemically equivalent to both the sodium carbonate and the sodium suld, may be thus added if desired. When such a large amount of ammonium sulnte is added, some carbon dioxide maybe driven oli along with am- .1

monia and a'volatile sulfid, and some or substantially all of the sodium carbonate be thus converted into sodium sulte. When ammonium sulte is added to such a solution in an amount which is just chemically equivalent to the amount of sodium suld, or a lesser amount is added, it is difficult if not impossible to remove from the solution substantially all of the suld-sulfur of the sodium suld as a volatile suld. By adding a considerably larger amount o ammonium sulsolution is maintained substantially non-acid in character until the `desired amount o suliid-sulfur has been removed from the solution as a volatile suld.

After such treatment by means of ammonium j suliite and after sullid-sulfur has been removed as a volatile suld and substantially all ammonia has been removed from the solution, the resulting solution may be given such further treatment as necessary or desired in order to form a regenerated cooking liquor. For example, the resulting solution may be used to absorb sulfur dioxide from gases obtained by burning sulfur or/and a suitable suliid, and the resulting solution may be suitably cooled if needed or desired prior to further suliiting. In case the regenerated cooking liquor is to be alkaline to litmus and contain mostly sodium suliite (NazSOs), sodium carbonate (if any)y remaining in the solution after removal of sulfid-sulfur and ammmonia may be suliited even while the solution is warm or hot until the desired amount of sodium sulte has been formed from such remaining sodium carbonate. If the regenerated cooking liquor is to be strongly acid to litmus, the solution should be suitably cooled before completing the sulting treatment.

In carrying out the process in accordance with the embodiment described above, the hot solu- Y tion which is to be treated with the ammonium sulte may be placed in an iron tank provided with a suitable agitator and with a steam nozzle equipped with a valve so that the amount of steam employed for driving oiic volatile sulfid and ammonia may be suitably controlled. `Suitable means for creating a vacuum may be connected to the tank to assist in removing volatile products. The vessel or tank may be suitably enclosed but provided with means for collecting volatile sull-ld and'ammonia driven off from the solution and for conducting such volatilized materials, especially suliid-sulfur, toa combustion chamber, such for example as that customarily operated in conjunction with a sulfur burner. Such volatilized sulid-sulfur may be therein subjected to a regulated oxidation by means ofV heated air so as to convert suliid-sulfur into sultesulfur. The resulting gases are withdrawn from the combustion chamber and suitably cooled and ammonia and resulting sulnte are absorbed in cool water to form a cool and suitably concentrated solution oi ammonium sulte. Such solution may with advantage contain some ammonium carbonate or/ and free ammonia. This solution may have such additional supplies of carbon dioxide, ammonia and/or sulfur dioxide added thereto as may be necessary in order to provide the nedded or desired amount of ammonium suli'ite. and am.- monia or/and ammonium carbonate if any, for treating another batch or lot of solution containing sodium carbonate and sodium suliid such as described above.

If desired, the amount of ammonium suliite thus added to a soda solution such as referred to above, which is to be suliited thereby, may be i as large as is sufficient to convert sodium suliid into sodium suliite drive off volatile vsuliid and to convert a desired portion (e. g. a prenonderating portion) or even substantially all of the sodium carbonate into a sulfite of sodium, so that upon completion of the step of removing volatile suld and ammonia, the resulting solution may contain little if any carbonate of sodium and it may require relatively little if any additional suliiting, except such as may be needed in order to produce an acid cooking liquor when such is desired. Thus the amount of ammonium sulfite added to the sodium carbonate-sodium suliid solution may vary considerably. It is usually preferable to add somewhat more ammonium sulrite than is just chemically equivalent to the sodium suliid, when ammonium sulte is mainly or fully relied upon for the suliiting treatment, since by so doing sulfid-sulfur can be removed from the solution to a greater extent than when a relatively small amount of sulfite, such as am moniuin sulte for example, is employed.

As a specific example or" the operation of the process in which the solution containing sodium carbonate and sodium suld is treated with ammonium sulte, the following description is given. The furnace product, e, g., containing sodium carbonate and sodium suliid, is treated with water in such amount and at such temperature as to give a hot solution, for example around to deg. C., so that 1,500 gallons of liquor contain around 2,245 pounds of sodium carbonate (Na-2G03) and around 824 pounds of sodium suld (NazS). This hot solution is placed in a suitable iron tank provided with an agitator and a steam nozzle and with means for collecting and removing volatile sulfid and ammonia to a combustion chamber such as described. A cool concentrated solution of ammonium sulfite, which contains about 1,838 to 2,450 pounds, more or less, of ammonium suliite, (NH4)2SO3, and also contains about 150 to 300 pounds, more or less, of free ammonia, (NHQOH, is added slowly and at a gradual rate and in a somewhat continuous manner, to the solution containing the sodium carbonate and the sodium suliid, while the solution in the tank is being vigorously agitated and steam is being introduced to maintain the solution at the boiling point, Volatile suld and ammonia are thus driven out from the solution and these are conducted to a suitable combustion chamber into which a regulated amount of air is suitably introduced. The resulting sulfur dioxide and ammonia, or ammonium sulite, are suitably cooled and then absorbed in cool water to form another lot or batch of cool and concentrated ammonium sulte solution. A suiiicient amount o` ammoniaand/or sulfur dioxide are added to this solution in any suitable manner, as may be needed, thus replacing losses of ammonia and sulfur dioxide. f Such reproduced ammonium sulte solution, together with free ammonia if needed or desired, is employed for treating'another batch of sodium carbonate and sodium sulfid in the foregoing manner; and the process maybe repeated over and over again.

The sodium-bearing solution, remaining after removal of volatile suld and ammonia therefrom, may still contain some carbonate of sodium (such as in the above specific example). This liquor may be thereafter subjected to aA further suliiting treatment, such as for example, by absorbing sulfur dioxide gas yin such liquor until any desired portion or even all remaining carbonate of sodium has been acted upon by the sulite radicle,

thereby forming more suliite of sodium. When theliquor has been sulted so that substantially all of the carbonate of sodium has been acted upon by the sul'lte radicle, the sultinfT may be discontinued. thereby providing a liquor which contains mostly sodium sulfite, the sodium content of which has been derived in part from the sodium suliid and in part from the sodium carbona-te. Such liquor may be modified needed or desired, such as by evaporation or by dilution with water, to provide regenerated cooking liquor lthe furnace product referred to above.

of the desired compositionand strength, for example so that the cooking liquor is about 3,000 to 3,500 gallons and contains around 4,000 pounds of NazSOs and a lesser amount of sodium thio- `sulfate if any. Such cooking liquor may be employed for a digestion of around 9,000 pounds (air-dry basis) of poplar Wood to produce chemical pulp in a manner disclosed in our former U. S. application Serial No.`481,147, led July 28, i921. The residual liquor resulting from such digesting operation may be the liquor which is evaporated and thus provide the residue which is to be furnaced under reducing conditions to'form And the complete cycle may be carried out a plurality of times Without the thiosulfate of sodium building up in the regenerated cooking liquor to a commercially prohibitive amount and without rendering'a commercially prohibitive amount of the sodium inactive or unavailable for the desired reaction or reactions in the digesting step of the cyclic process.

'Instead of discontinuing the sultingof the treated liquor, e. g. just at the point when all of the carbonate ofA sodium has been acted upon by the sulte radicle, the sulflting may be continued until an acid cooking liquor of desired ratio of free to combined sulfur dioxide composition is obtained, and the liquor may be diluted and cooled at any suitable time and in any suit able manner, and such cooking liquor may vary considerably in composition. Thus the cooking liquor may contain both normal sodium suliite and sodium bisulte, or it may contain sodium bisulte and sulfurous acid, or it may contain sodium bisulte Without either sulfurous acid or normal sodium sulte. When such regenerated cooking liquor contains sulfurous acid as Well as sodium bisulte, special care should be taken in its preparation to avoid the presence therein of more than a very small amount of thiosulfate. Thiosulfate is preferably absent from such an acid cooking liquor.

By maintaining the soda solution alkaline with a sufficient amount of free ammonia until substantially all suld-sulfur has been removed therefrom as a volatile suld, formation of thiosulfate in the liquor can be minimized, provided the sodium carbonate-sodium suld solution contains no loosely combined sulfurv at the time the suliite radicle is rst introduced, especially if the soda liquor is maintained at or around the boiling point throughout the period in which the sulte radicle is introduced and the sulte radicle is introduced in the manner outlined above.

Such acid cooking liquors may be employed for digesting Wood, etc., to produce chemical pulp or other suitable fibrous material, and the resulting residual liquor may be the liquor which is evaporated to yield the residue which is to be subsequently furnaced under reducing conditions to form the furnace product referred to above.

Instead of obtaining a furnace product such as described above, from residual liquor of a sulfite of sodium type of digesting treatment, the sodium suld or sodium carbonatesodium sulfid mixture may be obtained in any other suitable manner and from any suitable source. Thus residual liquor from an alkaline cooking operation with a cooking liquor which contains a sulfur-bearing compound of sodium, such as a cooking liquor which comprises sodium hydroxide and sodium sulnte or/and sodium suld, may be evaporated to remove Water and leave a residue which is thereafter furnaced to decompose organic matter andtoreduce any Oxy-sulfur sodium compound e. g. as lammonium sulte, in the manner disclosed above.

In a similar manner, wood, etc., may be cooked withy cooking liquor which comprises a carbonate Vof sodium or/and sodium thiosulfate together with a larger amount of sodium sulfite to form pulp or pulpy material and yield a residual liquor Which is thereafter evaporated and the residue furnaced under reducing conditions to form a furnace product from Which a solution con-taining sodium carbonate and sodium suld may be obtained.

Alternately, the Wood, etc., maybe cooked with liquor which comprisessodium sulfite and sodium suld-to form pulp or pulpy material and residual liquor, and the residual liquor may be evaporated and the residue furnaced under reducing conditions to form the furnace product, and the latter may be treated with Water to form the solution containing sodium carbonate and sodium suld. In any'such case the solution obtained from the -furnace V4product may be treated with the sulte radicle, e. g. With an ammonium sulte solution as pointed out above. Y

In orderto replace losses of soda in the operations, a sulfate of sodium may be added to the cycle at any suitable point, e. g., it may be added to residual liquor either before or after concentration thereof, and it is preferably added to w the cycle'prior to furnacing the residue left after evaporation of the residual liquor, and-sodium suld derived therefrom by the reducing furnace treatment; thus supplying both soda and suldsulfur to the cycle. YIn a later furnacing, some of the soda thus added is usually converted into sodium carbonate and appears as such in a furnace product.

Suchmethod of operation enables a portion of the pulp output of a mill to be produced by a sodium hydroxidetype of cooking operation and another portion to be produced by a suliite of sodium type of cooking operation, and the ratio of the amount produced by one type to the amount produced by another ytype may be regulated as desired by varying the amount of the sodium carbonate and sodium suld liquor which is causticized and the amount of such liquor which is treated so as to produce a sulite of sodium, as by a method herein outlined, for example. And soda lossesmay be replaced by a sulfate of sodium, thereby gaining not only soda but also some sulfur, sulfur of a sulfate of sodium being reduced to sulrld-sulfur and thereafter converted, at least in part, into sulte-sulfur and employed as a sulte in cooking liquor. In a companion application we are disclosing a process for such a multiple-liquor mill operation and such process is being claimed in such application.

The furnace product which contains the sodium carbonate and the sodium suliid may be produced in any suitable manner, it being advantageous to have a reducing condition in the presence of incandescent carbon in the furnacing operation so as to obtain a relatively large amount of sodium sulfidvin the furnace product. By using sodium sulfate or sodium acid sulfate to replace soda losses by adding such sulfate to other soium-bearing material and later carrying out the furnacing treatment under reducing conditions, a

lino

lias

,reiatively large amount of sodium suld can be obtained. When such sodium suliid, or a chosen portion thereof, is treated to remove suld-sulfur as a volatile suld and the latter is burned to form sulfur dioxide and this is employed in producing a sulte of sodium, use is made of both the soda content and the sulfur content of the sulfate of sodium in an advantageous manner.

The reducing furnacing operation may be carried out in a rotary incinerating furnace such as is ordinarily used for treatment of concentrated black liquor from the digesting operation of the conventional soda process. Or the furnacing treatment may be carried out by first removing water from residual liquor and forming a dry product by means of a rotary furnace such as is used in the conventional method of treating concentrated black liquor from the conventional sulfate process, and then treating the solids (including sufficient amount of carbonaceous material) in a furnace of a smelting type to produce a sodium carbonate-sodium sulfid melt. The melt may be dissolved in water, preferably While still hot from the furnace and either after or Without regulated oxidation treatment which is adapted by means of heated air, to convert a regulated amount of sodium suld into ksodium sulte. The

residual liquor from the digesting operation may, instead of the above, be given a preliminary evaporation treatment to produce a hot concentrated residual liquor;` and this hot concentrated liquor may then be sprayed into hot gases from the burning furnace to produce a dried and nely divided material, this dried material is then burned in a burni g furnace, e. g. as powdered fuel, under conditions regulated to decompose or burn organic matter and produce highly heated gaseous products of combustion and to form a furnace product containing sodium carbonate and sodium suld. Some carbonaceous material may, if needed or desired, be charged into the burning furnace in such manner that it is present with the melting or/ and molten material in the lower portion of the burning furnace, so as to aid in obtaining and maintaining a relatively large amount of sodium suliid in the melt which runs out from the furnace.

The highly heated products of combustion from the burning furnace may be used for generating steam by passing them through a suitable boiler, If desired hot concentrated residual liquor or solids may be sp ayed or blown into such a suitable burning furnace placed before the boiler, as pointed out in our former applications Serial No. 513,161 filed November 5, 1921 and Serial No. 248,959 flied January 23, 1928. K

furnace gases may be scrubbed, for example after having been passe through such a steam-boiler, Oxy-sulfur material regained therefrom. this purpose, such gases may be scrubbed either by means of residual liquor or/ and by ieans of a solution which contains either sodirun carbonate or sodium sull-ite or both sodium carbonate and sodium suliite. Such late ter solution or solutions may be derived from the furnace product as by using the liquor remaining after removal of sufid-sulfur, such as pointed out above. By scrubbing such furnace gases which carry oxy-srlfur material, such as sulfur dioxide, etc., they scrubbingl liquormay thus regain sulfur which has been dr 'en off from residual liquor or from a residue during the furnacing treatment of sodium-sulfur material derived from residual liquor. Thus the hot gases coming from the-steani-boiler may be scrubbed with residual liquor, thereby effecting an evaporation of Water and in some cases regaining some soda and/ or some ox'y-sulfiu1 material e. g. sulfur trioxide carried by the gases; and some sulfur dioxide may be transferred from the residual liquor to the gases, especially if the residual liquor be converted into finely divided dry material by spray evaporation, and provided it contained considerable sulte. The relatively cool gases which result may then be subjected to a scrubbing treatment by means of liquor containing sodium sulfite or sodium carbonate or both sodium sulte and sodium carbonate, and such scrubbing treatment may regain some sulfur dioxide from the gases, the amount depending upon the sulfur dioxide content of the gases and upon the conditions maintained during the scrubbing treatment.

It is advantageous to regulate the scrubbing treatments so that most if not all of the soda and sulfur trioxide carried by the gases coming from the steam-boiler are recovered by the residual liquor or the concentrated product which may be derived therefrom by such scrubbing and evaporation treatment therewith, and to transfer as much as feasible of the sulfur dioxide content of the residual liquor to the gases, and then to regain such released sulfur dioxide as Well as such sulfur dioxide as be present in the furnace gases as they come from the steam-boiler, in the sodium sulfite or/and sodium carbonate liquor referred to above. Such sulfur trioxide as is removed from the gases by means of residual liquor or resulting powdered material if any is delivered into the furnace along with the other material and can thus undergo a reducing treatment to form sodium sulfid, while the sulfur dioxide regained from the gases in the other type of liquor is available for cooking liquor or other purposes described herein. The latter type of liquor, after being used as a scrubbing liquor, may be suitably modified, if needed or desired, and then used for cookinfr Wood, etc., whether it be alkaline, neutral or acid to litmus, depending upon the degree to which the liquor was sulfted during or subsequent to the scrubbing treatment. Such liquor can also be used for other purposes, such as, for example, for reacting by virtue of dissolved sodium bisulte, with a liquor' which contains some free ammonia so as to provide a solution (alkaline to litmus) which contains both sodium sulte and ammonium sulte and may still contain some free ammonia. This solution may then be used to treat some sodium carbonate-sodium suld solution obtained from a furnace product of the cycle.

Where volatile gases, driven off from the soda solution, carry both hydrogen sulfide and ammonia, with the ammonia in much larger amount than the chemical equivalent of the hydrogen i sulde, burning of the hydrogen sulde Will yield gases Which carry ammonia in excess of that necessary to combine with the sulf' r dioxide thus formed. The method outlined above provides for making good use of some of the excess ammonia. When such ammonia and sulfur dioxide are absorbed in cool Water, the solution may contain some ammonium carbonate in addition to ammonium sulnte, some carbon dioxide having been released from sodium carbonate and removed from the solution along with the ainnonia and hydrogen sulfide. Sodium bisulte can react with some of the ammonium carbonate to ammonium sulfite and drive out some of the carbon dioxide. if desired, such solution may still contain some ammonium carbonate when it is added tothe sodium carbonate-sodium sulde solution. Upon heating of the resulting admixture .of solutions, carbon dioxide as Well as hydrogen sude and ammonia will be driven oli as volatile'mate'- rials.

Before adding ammonium sulte solution to ythe sodium carbonate-sodium suliid solution it may, if desired, be treated with a small amount of lime so as to convert some, or substantially all, of the ammonium carbonate into free ammonia and remove the carbondioxide radicle from the solution in the former calcium carbonate; but care should be exercised to avoid adding too much lime over that chemically equi-aient tothe carbon dioxide content of the solution as this may remove too much suliite radicle from the liquor as calcium sulte (CaSOa). The amounts and proportions ofsodium sulfite and ammonium sulte, with or without ammonia, etc., mayk vary considerably; thus either ammonium suliite or sodium suliite may be present in preponderatingr amount in the resulting solution.` v

Another advantageous method which may be 'employed for treatingsodium carbonate-sodium suld liquor derived from the furnace product by treating it with water, comprises using some` alkaline earth sulte, eg., magnesium sulfite (MgSOa), either alone or together With ammonium sulte, for producing sodium sulfite. When the process is thus, carried out with magnesium sulte, the chemical action is similar to that which takes place in the case of ammonium sulnte, in: that the magnesium sulnte formed in the solution is decomposed to give la volatile sulfide and a basic compound of magnesium. The former is driven ofi by boiling while the latter is precipitated. However, the presence of the base, even though it is in parta precipitate, helps to keep the solution alkaline and thereby to prevent the formation of sodium thiosulfate.

Ammonium suliite and magnesium sulte, and/or 'calcium suliite (CaSOs), with some free ammonia, if needed or desired, may be used to treat the hot concentratedsodium carbonate-sodium suld solution, and the solutionniay advantageously be heated to boiling prior to introducing the subite radicle andmainta'ined at or near the boiling point during the Ventii'e time occupied 'in introducing the sulfiteradicle or until the sulfidesulur is substantially all removed from the solution. For example, the sulite radicle may be introduced into thejhot soda solution at a slow rate' and hydrogen sulnd may beV removed from the liquor substantially as fast as it is formed. A volatile suld,-t'ogether with some ammonia, if ammonium suliitcorfreo ammonia has been used, will be driven out from the liquor. These may be conducted tothe combustion chamber and the suld--suliur burnedto sulte.

The ratio of ammonium sulte to inagnesium sulte and/ or calcium suliite may vary considerably, butit is an advantage to employ no more calcium sulte than is equivalent to the sodium carbonate, and to depend on either ammonium sulte or magnesium sulte or a mixture thereof to convert sodium suld into sodium sulte and drive out hydrogen sulfid. rEhe amount of ammonium suliite used may be less than or equal to or larger than that amount which is chemically equivalent to the sodium sulfid. vlll/"nen magnesium sulte is used for sulting the sodium carbonate, it may be converted into a carbonate f of magnesium, forming a precipitata and sodium suli'lte will be produced. The amount of magmaints-Lined dist nesium sulte' which may be employed, .either over that needed to remove all of the carbon dioX- r ide radicler away from the sodium carbonate, may or may not be used` Ir anexcess of magnesium sulte be used, it will appear to some extent in the solution. kDuring the formation and removal or volatile sulid, the solution advantageously is -Uly alkaline to phenolphthalein substantially throughout, is kept concentrated and at or around the boiling point, and is agitated, thus keeping the amount of hydrogen sulnd in the liquor at any instant down to itssubstantial minimum.

It is an advantage or the use of magnesiuml sulte that the precipitate which is formed assists materially in clarifying the solution. This eiect is particularly advantageous when the precipitate consists at least in part of magnesium hydroxide. i

After the suld-sulfur has been eliminated from the liquor to the desired degree, or at any suitable time prior thereto, the precipitated material (comprising carbonate of magnesium or/ and calcium carbonate) is separated from the liquor and kmay be again used to form morev alkaline-earth metal sulte or sultes. Such sulrlte or sulrites maybe reused in a similar manner. In order to convert the precipitate into a'v sulrite orsultes, as the Ycase may be, a solution of sodium acid sulnte containing the re-` quired amount of available sulfur dioxide may "'r be admixed with the precipitate and agitated therewith until substantially all of the sodium is pesent as normal sodium sulfite and all or nearly all of the alkaline-earth metal compound Yor compounds have been converted into normal sulte or suli'ltes; The slurry may be heated, if desired, prior to adding it to a solution of sodium carbonate and sodium suld, in order to remove any dissolved or loosely combined carbon dioxide.

In some cases, the amount of alkaline earth metal sulte employed may be such that an amount of ammonium sulfite equal to or less than that chemically equivalent to the sodium sulnd may be employed, or ammonium sull-ite may be entirely dispensed'vvithand the sulting be effected by magnesium sulte alone, in which instances some of the magnesium may be converted into a suliid of magnesium which compound `Will be decomposed at the boiling tempsature of theliquor, formingfmagnesium hydroxide and volatile sulld-being removed from theA liquor. v, i

Some free ammonia may, if desired or needed, be maintained in the liquor 'until substantially all of the volatile suliid has been removed from the liquor, thus aiding in the prevention of thiosulfate formation. g

Various mixtures of magnesium suliite and ammonium sulrlte, either with or without calcium sulnte, and either with or Without free ammonia,

may be employed for the treatment or" the sodiumV carbonate-sodium suld solution. In some cases, most ifl not allk of the sulnting of the sodium compounds can be eiected by magnesium sulte,

either alone or in conjunction with calcium sullte, and little or none eiected by ammonium sulte, care being taken to maintain the solution sufficiently alkaline to phenolphthalein, e. g.

with a suitable hydroxyl compound or compounds,r

until the desired amount of suld-sulfur has been removed as a volatile suld, using care to maintain the liquor at or near the boiling point While it contains any appreciable amount of volatile suld. When little or no ammonium suli'ite is employed, magnesium sulite may be used in an amount which is just about chemically equivalent to the sodium suld; but there is an advantage in using somewhat more magnesium sulte than this, e. g. an amount ranging up to that which is chemically equivalent to both the sodiumcarbonate and sodium suld, although an excess can be used if this is desired.

Calcium suliite can be used to sulfite any portion or substantially all of the sodium carbonate and after this has been done magnesium sulte can be used to react With sodium sulfid and remaining sodium carbonate, if any. The'precipitate in such cases comprises a carbonate of magnesium or/and magnesium hydroxide, the latter apparently resulting from decomposition of magnesium suld with liberation oi hydrogen sulde and formation of the relatively insoluble magnesium hydroxide.

In case magnesium hydroxide is not present in suicient amount or hydroxyl is not otherwise present in adequate concentration to prevent formation of thiosulfate in prohibitive or undesired amount, good results may be obtained by retaining in the solution enough free ammonia to maintain it basic. A relatively small amount of ammonia may be thus used, most or all of the sulting being carried out by means of magnesium sulfite either alone or subsequent to treat'- ment of sodium carbonate with calcium suliite. The liquor should be kept hot and suiiiciently alkaline to phenolphthalein; and carbon dioxide or/and hydrogen suliid should not beY permitted to build up in the solution to an objectionable or a prohibitive point.

A solution comprising sodium sulte and sodium suld, such as results from treatment of a sodium carbonate-sodium suliidliquor by means of calcium suliite, for example, in amount just about equivalent to the sodium carbonate, may be treated with a mixture of calcium sulte and magnesium sulte, the latter in amount substantially equivalent to ora little more than is equivalent to the sodium suliid; and volatile suliid then driven oi from the heated liquor. The precipitate may then be separated from the liquor and the calcium sulfite contained therein may be used to react with sodium carbonate in a liquor which also contains sodium suliid, and the resulting liquor may be separated from the solids and then treated by a mixture of calcium suliite and magnesium sulte. The mixture of calcium carbonate and the basic magnesium precipitate may be sulted, as pointed out above, by means of sodium acid sulte for example, and such formed vcalcium sulte and magnesium suliite employed in the foregoing manner. Dolomitc material may be thus employed in the process.

A now sheet illustrative of the process of the invention is shown in the accompanying drawing, With the various operations and apparatus illustrated in a conventional manner and with the successive steps and sequence of operations, supply of materials and removal or recirculation of materials, indicated by arrows, in a conventional manner.

From the foregoing it will be clear, that anA oxysulfur compound of sodium (such for example as sodium sulfate, sodium bisulfate, sodium sulite, sodium bisulfite, sodium thiosulfate, sulfoorganic' compounds vof sodium, etc., or mixtures of two or more thereof) may be subjected to a reducing treatment in the presence of incandescent carbon, thereby forming a furnace product including sodium suld; that sodium content of sodium suld thereof may be converted into an oxysulfur compound of sodium and sulfur content thereof may be removed from the latter oxysulfur compound of sodium as a suld; and that the latter oxysulfur compound of sodium may be subjected to a treatment including a reducing treatment adaptedto form sodium sulfid. As an illustration, sodium sulte or/and sodium sulfate may be admixed with carbonaceousmaterial and furnaced under highly reducing conditions to form a furnace product containing a large portion of its sodium content the form of sodium suld. Such sodium suld may be dissolved in Water to form a solution and this solution may be treated with a suitable oxysulfur compound of magnesium (e. g., MgSO3 or/and MgSO4) in amount sufficient to convert substantially all of the sodium content or" the sodium suld into the corresponding sodium compound (e. g., sodium sulfite or/and sodium sulfate), and the solution may be boiled to drive out substantially all of the released hydrogen suld, thereby forming a precipitated material including a compound of magnesium. The precipitated material can be Washed and dried and sold, or it can, in whole or in part, be used to react with SO2 carried by the gases to form magnesium sulte or/and with S03 to form magnesium sulfate. The process may be repeated tWo or more times.

We claim:

l. The method of treating residual liquor from the cooking of wood with a solution including a sulte of sodium, which comprises furnacing constituents of the residual liquor under conditions adapted to provide sodium carbonate and sodium sulfid, dissolving such sodimn compounds, adding ammonium sulte to the resulting solution, and boiling the solution to remove ammonium carbonate and ammonium sulfid therefrom.

2. The cyclic process for producing sodium'sulfte from sodium sulfid, which comprises adding Vammonium sulte to a solution of the sodium suld, boiling the solution to remove ammonia and a suld, leaving sodium sulte in solution, burning sulfur so removed, J(hereby forming a mixture of sulfur dioxide and ammonia, absorbing said material to form a solution of ammonium sulte, and utilizing such ammonium sulte for treating sodium suld. n Y

3. The method of producinga solution containing sodium sulfite from a solution containing sodium suliid which comprises treating such solution .Y

5. The method of producing a solution containing sodium sulte from a solution containing sodium sulfld which comprises treating such solution With an alkaline earth metal sulite selected from the group composed of calcium sulte and magnesium at a temperature which Will drive off hydrogen suld and precipitate an insoluble alkaline earth metal compound.

6. The method of producing a solution containing sodium sulte from a solution containing sodium suld which comprises adding to such solution a sulte selected from the group consisting of calcium, magnesium, and ammonium sulfites to react with the sodium suld to form sodium sulte and a volatile suld, and removing the volatile suliid from the solution.

7. The method of producing a solution containing sodium sulte from a solution containing sodium suld vwhich comprises adding to the solution While it is maintained substantially nonacid in character a sulte selected from the group consisting of calcium, magnesium, and ammonium sultes to react with the sodium suld to form sodium sulfite and a volatile sulld, and removing the volatile sulfid from the solution.

8. The method of producing a solution containing sodium sulte from a solution containing sodium suld which comprises treating such solution While maintained under substantially nonacid conditions with a sulte selected from the group consisting of calcium, magnesium, and ammonium sultes and maintaining the solution at a temperature sufficient to remove hydrogen sulid from the solution.

9. The method of producing a solution containing sodium sulte from a solution containing sodium sulid and sodium carbonate which comprises treating such solution with a sulfite of ammonium at a temperature which will drive off a volatile suld from the solution and leave a solution containing sodium sullte.

10. The method of producing a solution containing sodium sulte from a solution containing sodium suld and sodium carbonate which comprises treating such solution With a sulte selected from the group consisting of calcium, magnesium and ammonium suliites to convert the sodium carbonate and sodium suld into sodium sulte and form a Volatile sulfid, and maintaining the solution at a temperature sufficient to remove the volatile sulfid from the solution.

11. The method of producing a solution containing sodium sulte which comprises treating a hot solution containing sodium carbonate and sodium suld with ammonium sulte, the temperature being maintained suiciently high to drive off the suld sulfur as a volatile sulfld.

12. The method of producing a solution containing sodium sulte from a solution containing sodium carbonate and sodium suld Which comprises treating such solution While maintained at a temperature around the boiling point With ammonium sulte and excess ammonia and agitating such solution to promote the removal of the suld sulfur as a volatile suld.

13. The method of producing a solution containing sodium sulite from a solution containing sodium carbonate and sodium suld which comprises adding to a hot concentrated solution containing sodium carbonate and sodium suld ammonium sulte with excess ammonia in amount sufficient to react with the sodium sulfid to form sodium sulte and a volatile sulfid, and promoting the removal of the volatile suld by boiling and agitation of the solution.

14. The method of producing a regenerated cooking liquor containing a sulfite of sodium from a furnace product containing sodium carbonate and sodium sulfid which comprises treating a solution of the sodium carbonate and sodium suld with a suliite selected from the group consisting of calcium, magnesium and ammonium sultes to react with the sodium suld to form sodium sulte and a volatile suld, maintaining the solution substantially non-acid and at a temperature which Willpromote the removal of the volatile suld and subsequently subjecting the resulting solution containing sodium sulte and sodium carbonate to sulting with sulfur dioxide to convert the sodium carbonate into sodium sulte.

15. The method of producing a solution containing sodium sulte from a solution containing sodium suld which comprises treating such solution with ammonium sullite under conditions to form sodium sulte and a volatile suld, removing the volatile sulid together with ammonia from the solution, oxidizing the volatile sulfld to form sulfur dioxide in admixture with ammonia, absorbing the resulting gases in Water to form a solution of ammonium sulite and using such solution for the treatment of further amounts of solutions containing sodium suld.

16. The method of producing a solution containing sodium sulte from a solution containing sodium suld which comprises treating such solution with ammonium sulte and an alkaline earth metal sulte selected from the group composed of calcium sulte and magnesium sulte at a temperature sufficiently high to orm and remove the suld sulfur as a volatile suld and form a solution containing sodium sulte and an insoluble alkaline earth metal compound as a precipitate.

17..The method of forming a solution containing sodium sulte from a solution containing sodium carbonate and sodium suld which comprises treating such solution with ammonium sulte and an alkaline earth metal sulte selected from the group composed oi calcium sulite and magnesium sulte at a suiiiciently high temperature to drive off sLLlid sulfur in the form of a volatile sulfid and to form an alkaline earth metal carbonate, and removing the volatile sulfid and the alkaline earth metal carbonate from the sodium sulte solution.

18. The method of treating residual liquor from the cooking of Wood with a solution including a sulte of sodium which comprises furnacing constituents of the residual liquor under conditions adapted to provide sodium carbonate and sodium sulid, dissolving such sodium compounds, adding to the resulting solution while maintained under substantially non-acid conditions a sullte selected from the group consisting of calcium, magnesium and ammonium suliites, maintaining the solution at a suiciently high temperature to remove a volatile suld from the solution, and converting the sodium carbonate into a sulte of sodium by means of available sulfur dioxide.

19. The method of treating solutions that contain sodium suld, which comprises admixing therewith an oxysuliur compound selected from. the group composed of ammonium, calcium and magnesium sultes and magnesium sulfate, and heating the liquor to remove a volatile suld therefrom.

LINN BRADLEY. EDWARD P. MCKEEFE. 

